An organic EL element is an element that emits light in proportion to a current quantity. Therefore, in order that the organic EL element can maintain constant luminous intensity without depending on an external power supply, it is necessary to flow a constant current through the organic EL element. Moreover, the organic EL element is also a semiconductor device that exhibits diode characteristics, and has a possibility to be broken in such a manner that a value of the current rises owing to generated heat (Joule heat), and accordingly, it is necessary to flow the constant current therethrough. Accordingly, an organic EL device in which a constant current circuit is provided for the organic EL element has been proposed.
Patent Literature 1 discloses an organic EL display device including an organic EL element that has a driver circuit having a constant current circuit for flowing a constant current of several micron amperes. In this organic EL display device, a pair of driver circuits are arranged along two sides on a transparent substrate. The organic EL element and the driver circuit including the constant current circuit are integrated with each other as described above, whereby it has been possible to realize reliability enhancement, miniaturization, thinning and cost reduction of the organic EL display device.
Note that, in this organic EL display device, light emitting portions arranged in a matrix form are allowed to emit light by the driver circuits, whereby an image is displayed thereon.
Moreover, the organic EL lighting device includes the organic EL element having the diode characteristics. When the current flows through the organic EL element in a forward direction, the organic EL element emits light proportional to a value of the current. Hence, in the case of driving the organic EL lighting device by an alternating current power supply, blinking light emission occurs in accordance with a cycle of an alternating current. Here, a cycle of a usual commercial power supply (100V to 220V) of 50 Hz to 60 Hz is approximately 16.7 msec to 20.0 msc. This cycle is extremely long in comparison with a response speed of the organic EL device, which is from several nanoseconds to several ten nanoseconds. Therefore, even in the case of using an inverter or the like, blinking of the organic EL element cannot be suppressed, and hence, there has been a problem that the blinking concerned looks flickering to human eyes, resulting in uncomfortableness.
In this connection, Patent Literature 2 discloses an organic EL lighting device in which a rectifier circuit is connected between the alternating current power supply and the organic EL element. In this organic EL lighting device, the current is supplied to the organic EL element through the rectifier circuit, whereby it has been possible to suppress the blinking of the organic EL element.